.submenu {
position: absolute;
top: 100%;
left: 0;
display: none;
z-index: 1;
background-color: #fff;
box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
height: auto; /* 新增，高度自适应 */
}

.submenu ul {
list-style-type: none;
margin: 0;
padding: 0;
display: flex;
flex-direction: column;
width: 100%;
align-items: stretch; /* 父容器高度自适应，子容器也需要适应 */
justify-content: space-around; /* 新增 */
}


.submenu li a {
display: block;
color: #707070;
text-decoration: none;
box-sizing: border-box;
width: 100%;
text-align: center; /* 新增居中 */
}

.submenu li a:hover {
background-color: #f2f2f2;
}

.nav .item .submenu {
display: none;
position: absolute;
top: 100%;
left: 0;
min-width: 100px;
}